1. Field of the Invention
The present invention relates to a production method of wood cement board that has a pattern of recesses and projections on its surface.
2. Description of Related Art
Wood cement boards are produced by forming a mat using a raw material mixture in which a hydraulic material, a silica-containing material, a wood reinforcement, and as needed, other materials are blended, and then pressing the mat, followed by hardening and curing. Such wood cement boards are widely used as housing members such as exterior building materials and backing materials of tiles. Various patterns formed by recesses and projections, such as a brick pattern and joint grooves, are created on the surface of wood cement boards for use as exterior building materials in order to achieve an improved appearance.
Recently, for a further improved surface design, there is a demand for acute-angled and deep recesses and projections.
Wood cement boards for use as backing materials for tiles need to be provided with fixing portions formed by acute-angled and deep recesses and projections on their surface for securing the tiles.
Wood cement boards are produced by forming a mat using a raw material mixture in which a hydraulic material, a silica-containing material, a wood reinforcement, and as needed, other materials are blended, and then pressing the mat, followed by hardening and curing.
According to this aspect of the present invention, the hydraulic material may be cement such as portland cement, blast furnace cement, silica cement, fly ash cement, or alumina cement, the silica-containing material of the invention may be silica sand, silica stone powder, silica fume, blast furnace slag, fly ash, shirasu balloon, pearlite, or the like.
In an existing situation of water, the silica-containing material stiffens with the cement by hydration reaction.
And the wood reinforcement of the invention may be wood meal, wood fiber, pulp, wood fiber bundle, wood wool, wood chip, bamboo fiber, hemp fiber, or the like.
The bulky wood fiber bundle that is branched and/or curved and/or bended is particularly desirable.
In addition to the above-described raw materials, it is possible to include, as raw materials, an active lime-containing material such as gypsum dihydrate, gypsum hemihydrate, anhydrous gypsum, hydrated lime, or quick lime, a hardening accelerator such as magnesium chloride, calcium formate, magnesium sulfate, calcium chloride, calcium sulfate, sodium aluminate, potassium aluminate, aluminum sulfate, or water glass, mineral powder such as vermiculite, bentonite, wollastonite, or attapulgite, a water repellent agent such as wax, paraffin, or silicone, a reinforcement such as synthetic resin emulsion, as well as foamable thermoplastic bead, and foamed plastic.
Examples of the method for forming recesses and projections on the surface of a wood cement board include a method in which an embossing roll having an engraved pattern of recesses and projections is rolled on the surface of a half-hardened mat that has not been pressed, while applying pressure, thereby forming the desired pattern of recesses and projections on the surface, a method in which the surface of a wood cement board that has undergone a hardening and curing process is subjected to cutting such that a pattern of recesses and projections is formed on its surface, and a method in which a template having a pattern of recesses and projections is placed on the surface of a mat that has not been pressed, followed by pressing the mat together with the template.
However, with the method using an embossing roll, it is difficult to form acute-angled and deep recess and projection shapes.
The method in which the surface of a wood cement board is subjected to cutting requires a cutting process, and therefore involves additional equipment cost and time, leading to poor production efficiency. Moreover, defective products tend to be produced as a result of cutting failure in the cutting process.
The method using a template can form acute-angled and deep recess and projection shapes. However, the mat on which the template is placed has an approximately uniform thickness and an approximately flat surface, and therefore, the recesses have a high specific gravity and the projections have a low specific gravity. Due to this specific gravity difference between the recesses and the projections, cracking tends to occur in the wood cement board during a hardening and curing process, a drying process, a transportation process and so on, and a coating material is absorbed into the substrate of the wood cement board during a coating process. This results in the problems of a significant reduction in the strength, the water resistance, the freeze resistance, the weatherability and the like of the wood cement board, an increase in the amount of the coating material required, and nonuniform coating.
As one remedy for the above-described problems, there has been proposed a method in which a mat layer is formed by dispersing a raw material mixture with a plurality of partition plates placed on predetermined areas, and then removing the raw material mixture present on the partition plates, thereby forming a mat having recesses on the predetermined areas, and an upper template provided with projections corresponding to the portions on which the recesses are formed is pressed down from above the thus formed mat, followed by hardening and curing (JP 2001-150421 A).
However, the method disclosed in JP 2001-150421A requires the operation of arranging partition plates, and also the operation of removing the partition plates, and therefore has reduced production efficiency.
Moreover, there will be an extra initial cost since various partition plates need to be prepared depending on the depth, the width, and the length of the recesses. In the case of forming a pattern having a large number of recesses or a pattern having recesses of various shapes, the operation is more complicated, which results in a further reduction in the production efficiency.
Also in the case of forming recesses that have a long shape, such as those longitudinally traversing the surface of a wood cement board, or that have a wide shape, the workability is reduced and the production efficiency is poor.
The present invention has been made in order to solve the above-described problems, and it is an object of the invention to provide a high production method of the production efficiency for a wood cement board that has a pattern of recesses and projections